Shedding Dead Leaves

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Science  08 Oct 2010:
Vol. 330, Issue 6001, pp. 153
DOI: 10.1126/science.330.6001.153-b
CREDIT: ANTONELLI ET AL., PROC. R. SOC. LONDON SER. B 277, 10.1098/RSPB.2010.1145 (2010)

Historically, New Zealand had flourished without terrestrial mammalian fauna until the relatively recent arrival of humans. As a consequence, many plants have evolved in the absence of selective pressures generally attributed to mammalian lineages. One such example is the grass family, which is believed to have coevolved elsewhere with grazing ungulates, such as modern-day horses. Many grasses show specific adaptations to grazing, including the retention of old leaves, which makes the live leaves less readily accessible to grazing mammals. Antonelli et al. demonstrate that many members of the danthonioid group of grasses of New Zealand (such as Rytidosperma pulchrum, above) have gained the ability to lose dead leaves, a process known as abscission, which is a relatively rare trait that occurs in only ∼3% of graminoids worldwide and that allows plants to generate more biomass. The authors attribute this pattern to the lack of selective grazing pressures by mammals and demonstrate how this trait is correlated with species radiations in New Zealand but not in other endemic floras. These data suggest that release from a selective pressure can lead to species radiations and contribute to the uniqueness of biotas.

Proc. R. Soc. London Ser. B 277, 10.1098/rspb.2010.1145 (2010).

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